I started from tabs that are not on the beginning of lines, and in
several places I did further cleanings.
If you're worried about knowing who wrote some code, for example, if you
get to this commit in "git blame", then note that you can use the "-w"
flag in many git commands to ignore whitespaces. For example, to see
per-line authors, use "git blame -w <file>". Another example: to see
the (*much* smaller) non-whitespace changes in this (or any other)
commit, use "git log -p -w -1 <sha1>".
Also, use keywords for `make-pen' and `make-brush'.
Adding `make-pen' and `make-color' creates many conflicts among
teaching libraries, such as `2htdp/image'. These are easy to fix
up in the tree, but adding such obvious names to `racket/draw'
may create other compatibility problems, so we might have to reconsider
the names.
In consultation with Asumu.
